The invention relates to an energy supply system and to a method for actuating coupling devices of an energy storage device, in particular an energy storage device comprising a modular battery system.
It would appear that in the future electronic systems which combine novel energy storage technologies with electrical drive technology or with electrical supply grids will be used increasingly both in stationary applications, such as wind turbines or solar systems, for example, and in vehicles, such as hybrid or electric vehicles and ships.
Feeding single-phase or polyphase current into an electrical machine or electrical supply grid is generally effected by means of a converter in the form of a pulse-controlled inverter. For this purpose, a DC voltage provided by a DC link can be converted into a single-phase or polyphase AC voltage, for example a three-phase AC voltage. The DC link is in this case fed from a string of battery modules connected in series. In order to be able to meet the requirements in respect of power and energy which are set for a specific application, a plurality of battery modules are often connected in series in a traction battery.
The publication U.S. Pat. No. 5,642,275 A1 describes a battery system with an integrated inverter function. Systems of this type are known under the name multilevel cascaded inverter or battery direct inverter (BDI). Such systems comprise DC sources in a plurality of energy storage module strings, which are connectable directly to an electrical machine or an electrical grid. In this case, single-phase or polyphase supply voltages can be generated. The energy storage module strings in this case have a plurality of series-connected energy storage modules, wherein each energy storage module has at least one battery cell and an associated controllable coupling unit, which makes it possible to interrupt the respective energy storage module string or to bypass the respectively associated at least one battery cell or to switch the respectively associated at least one battery cell into the respective energy storage module string, depending on control signals. By suitable actuation of the coupling units, for example with the aid of pulse width modulation, suitable phase signals for controlling the phase output voltage can also be provided, with the result that it is possible to dispense with a separate pulse-controlled inverter. The pulse-controlled inverter required for controlling the phase output voltage is therefore integrated in the BDI, so to speak.
Similar systems are disclosed in the publications DE 10 2010 027 857 A1 and DE 10 2010 027 861 A1, which disclose, for example, battery direct inverters comprising a plurality of battery module strings, which are connectable directly to an electrical machine.
BDIs generally have a higher degree of efficiency and a higher degree of failsafety in comparison with conventional systems. The failsafety is ensured, inter alia, by virtue of the fact that defective battery cells, failed battery cells or battery cells which are not operating at full capacity can be removed from the energy supply strings by suitable bypassing actuation of the coupling units. The phase output voltage of an energy storage module string can be varied, and in particular adjusted stepwise, by corresponding actuation of the coupling units. The graduation of the output voltage in this case results from the voltage of a single energy storage module, wherein the maximum possible phase output voltage is determined by the sum of the voltages of all of the energy storage modules in an energy storage module string.
In order to adjust an output voltage of an energy storage module, a pulse-width-modulated (PWM) actuation of the coupling units can take place. As a result, it is possible to output a desired average as energy storage module voltage by targeted variation of the switch-on or switch-off times.
A requirement for BDIs or modular energy storage devices consists in actuating the coupling units of the individual energy storage modules quickly, flexibly, reliably, with energy efficiency and at low cost. As the number of energy storage modules increases, this requirement becomes increasingly difficult.
Therefore, there is a need for actuation for coupling devices of modular energy storage devices in which the power electronics of the individual energy storage modules can be actuated with a high level of accuracy, at high speed, with as much flexibility as possible and with little implementation complexity being involved.